The study of amphetamne (AMPH) induced dopamine (DA) release in bipolar disorder will explore abnormalities in presynaptic dopamine release mechanisms as well as study post-synaptic DA receptors. The general aim of this study is to evaluate potential neurochemical correlates of AMPH challenge inpatients with bipolar disorder currently stable on the mood stabilizer--lithium. Patients with bipolar disorder and healthy controls matched for age, sex and ethnic origin will undergo one SPECT experiment with the D2 tracer [123I]IBZM.